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Golden Alga

Prymnesium parvum

Management Options

Mechanical/Physical Control Options

Golden alga (Prymnesium parvum) cannot be mechanically or physically controlled, except by replacing the pond water. Exchange of water from a well or other source that does not contain the algae bloom will dilute the golden algae in the pond. This is not a practical option for most pond owners unless their ponds are very small and they have wells close by. Downstream release of golden alga may cause a fish kill and liability could be an issue.

Golden alga (P. parvum) prefer brackish or slightly saline waters. If pond water can be maintained fresh either through the addition of well or surface water then golden algae growth may be suppressed or eliminated.

Non-toxic dyes or colorants prevent or reduce aquatic plant growth by limiting sunlight penetration, similar to fertilization. Aquashade, Blue Springs, and Crystal Blue are examples of non-toxic dye and other products are available. However, dyes do not enhance the natural food chain and may suppress the natural food chain of the pond.

Many types of mechanical removal devices are available that cut or chop up aquatic weeds. It is important to remember that many submerged plants regrow from fragments, so removal of cut fragments many be necessary to keep from spreading the unwanted plant. Companies that make cutters and rakes include but are not limited to Cutting Edge, Jenson Lake Mower, Midwest Aqua Care, and WeedRoller.

Physical barriers are also used to eliminate plants by shading the bottom. These work well for swimming areas, docks, etc. but must be kept clean of any buildup of sediment and debris. Lake Mat and Lake Bottom Blanket are examples of companies that makes these mats.

Biological Control Options

While many microscopic animals (zooplankton) eat planktonic algae there is no practical way to increase their populations, so no biological control is possible.

Chemical Control Options

The active ingredients that have been successful in treating golden algae include copper based compounds (E), sodium carbonate peroxihydrate (G), potassium permanganate (E), and ammonium sulfate (G). E = excellent, G = good

The key to controlling a golden algae bloom is to treat the algae before it becomes toxic or before it releases toxins. To do this the pond water has to be examined for the presence and density of golden algae. This examination takes a good microscope, a hemocytometer and knowledge of the organism. This service is currently being provided by:

The chemical treatments described below do not detoxify the golden alga toxin, with the exception of potassium permanganate. The algaecides below kill the P. parvum but the water will remain toxic until fresh water dilutes it out or it is broken down by natural processes over time (usually within a few weeks).

Copper Sulfate or “blue stone” is probably the most commonly used algal treatments because of its availability and low cost. Copper sulfate comes in several forms depending on how finely it is ground. Smaller crystals will dissolve easier than larger crystals. In very hard (>200 mg/L total alkalinity) water it is difficult to use copper sulfate because it quickly binds with the calcium, precipitates out of solution, and renders the copper ineffective as an algaecide. The toxin of golden algae is not detoxified by these algaecides.

All copper compounds can be toxic to fish if used above labeled rates and can be toxic in soft or acidic waters even at label rates. Before using copper is it best to test the pond water’s alkalinity and adjust copper treatments to alkalinity concentrations. For additional information on using copper sulfate see the SRAC #410 Calculating Treatments for Ponds and Tanks.

Cutrine Plus, K-Tea, Captain, and Clearigate are all chelated or compound copper herbicides that are effective on planktonic algae like golden algae. Other chelated or compound copper formulations are available but are not linked to this web site.

GreenClean, PAK27, and Phycomycin are Sodium Carbonate Peroxyhydrate (SCP) based herbicides. These are contact herbicides for control of some algae and have been shown to kill golden algae. Hydrogen peroxide is the active agent in this algaecide. SCP is not effective on the macroalgaes, Chara or Nitella, or on any higher plants. The toxin of golden algae is not detoxified by this algaecide.

Potassium permanganate is not a registered algaecide but an oxidizing agent. If used it will kill algae and neutralize the toxin. Potassium permanganate is usually used at 2 mg/L but a higher concentration may be required if the pond water has a high oxidative demand. High concentrations (in excess of 2 mg/L above the oxidative demand) may be harmful to fish and other aquatic organisms.

Ammonium sulfate is not a registered algaecide but a type of fertilizer. The ammonium ion of this compound is what kills the golden algae. The ammonium ion is also toxic to fish and many other aquatic organisms. Therefore, great care must be taken to apply this compound at the appropriate concentration. The appropriate concentration has to be calculated of each particular pond and per conditions of the pond immediate before application. Water quality tests for pH, temperature, and ammonia are necessary to calculate the concentration of ammonium sulfate to use.

For more information on golden algae and the use of potassium permanganate and ammonium sulfate to control it, see the TX Parks and Wildlife publication at:

One danger with any chemical control method is the chance of an oxygen depletion after the treatment caused by the decomposition of the dead plant material. Oxygen depletions can kill fish in the pond. If the pond is heavily infested with weeds it may be possible (depending on the herbicide chosen) to treat the pond in sections and let each section decompose for about two weeks before treating another section. Aeration, particularly at night, for several days after treatment may help control the oxygen depletion.

One common problem in using aquatic herbicides is determining area and/or volume of the pond or area to be treated. To assist you with these determinations see SRAC #103 Calculating Area and Volume of Ponds and Tanks.

Many aquatically registered herbicides have water use restrictions (See General Water Use Restrictions).

To see the labels for these products click on the name. Always read and follow all label directions. Check label for specific water use restrictions.

Cultivation Options

The golden alga (Prymnesium parvum) should never be promoted. For additional information on fertilizing ponds for beneficial algae see SRAC #471 Fertilization of Fish Ponds.